1. Field of the Invention
This invention relates to automatic lockout mechanisms for electrical equipment containers. More specifically, the invention relates to a system for preventing connection of electrical equipment within a cabinet unless the cabinet door is closed.
2. Description of the Related Art
Electrical equipment such as circuit breakers is typically housed within containers designed to prohibit access to the equipment at times when servicing the equipment would be unsafe. A circuit breaker for medium voltage applications will typically include male and female connectors for disconnecting the circuit breaker from the circuit prior to opening the circuit breaker""s container. Additionally, it is generally considered desirable to house such circuit breakers within an arc-resistant container. To qualify as arc-resistant, the door of the cabinet must be closed before the circuit breaker can be connected.
Other proposed interlock designs include interlocks that are locked or unlocked based on the position of the cabinet door""s handle. One such example includes a pivoting rod blocking rotation of the door""s handle when a fuse box assembly is not fully disengaged from its associated circuit. When the fuse box assembly is fully retracted, a pin on a carriage roller engages a camming surface on a rod, disengaging the rod from the door handle mechanism and permitting the door to be opened. Additionally, a slider prevents access to a threaded rod of a levering-in mechanism when the door""s handle is rotated away from the locked position, thereby securing the carriage in the retracted position. An interlock actuated by the position of the door itself may be more reliable than an interlock actuated based on the position of the door""s handle.
Another example of an arc-resistant cabinet includes a plurality of tabs on the cabinet doors positioned behind corresponding tabs on the edges of the cabinet""s door frame when the doors are closed. The interlocking tabs help the door resist an explosion inside the cabinet.
Yet another example of an interlock includes a key-actuated slider for securing a source circuit breaker in a test position. The key necessary for accessing the levering-in mechanism for the other breakers is secured within the lock of the source breaker unless the source breaker is locked in this test position, thereby cutting off current to the other breakers.
Therefore, there is a need for an improved interlock for electrical cabinets wherein the interlock mechanism is actuated by the position of the door itself, instead of the position of the door""s operating handle. Additionally, there is a need for an improved interlock having fewer components, greater reliability, and easier manufacture than previous interlocks.
The present invention is an automatically operating interlock for electrical cabinets, such as arc resistant circuit breaker cabinets. The interlock prevents connecting the circuit breaker or other electrical equipment within the cabinet unless the cabinet door is closed.
A typical circuit breaker for medium voltage applications is mounted on a carriage that is movable between a forward, disengaged position and a rearward, engaged position within the cabinet containing the circuit breaker. At least one pair of quick disconnects terminating in finger clusters protrudes from the rear of the circuit breaker, being dimensioned and configured to engage a pair of stabs at the rear of the circuit breaker""s cabinet when the circuit breaker is in the rearward position, thereby connecting the circuit breaker to the protected circuit. A typical medium voltage circuit breaker will use three pairs of mating stab/quick disconnect combinations. When the circuit breaker is moved to its forward position, the finger clusters are withdrawn from the quick disconnects, thereby disconnecting the circuit breaker from the circuit.
Moving the circuit breaker from one position to the other is accomplished by means of a threaded rod extending from the front to the rear of the cabinet. A levering in block engages the threaded rod so that rotation of the threaded rod pushes the levering in block either forward or rearward. The levering in block is secured to the carriage, so that rotation of the threaded rod thereby moves the carriage forward or backward. This process is known as levering in. The levering-in rod is turned by inserting a tool through an opening in the cabinet door to engage the end of the rod, which typically includes a hex drive. A levering-in locking bar surrounds the hex drive, and is spring-biased into a forward position blocking access to the hex drive. Inserting the tools through the hole in the cabinet door to engage the hex drive requires pushing the levering-in locking plate rearward as the hex drive is engaged.
The interlock includes a spring-biased locking plate reciprocating between a first position wherein the locking plate is immediately behind the levering-in locking plate, resisting rearward movement of the levering-in locking plate, and an unlocked position wherein the locking plate has been removed from contact with the levering-in locking plate, and permits movement of the levering-in locking plate. The locking plate is spring-biased towards its locked position. When the cabinet door is closed, a tab on the door engages a slot in the locking plate, thereby pushing the locking plate from its locked position to its unlocked position. Likewise, opening the door permits the locking plate to move under spring pressure from its unlocked position to its locked position. Access to the hex drive of the levering-in rod is thereby precluded unless the cabinet door is closed.
It is therefore an aspect of the present invention to provide an automatically operating interlock for electrical cabinets, preventing equipment within the cabinet from moving from a forward, disconnected position to a rearward, connected position unless the cabinet door is closed.
It is another aspect of the present invention to provide an automatically operating interlock for electrical cabinets that is actuated by the position of the cabinet door.
It is a further aspect of the present invention to provide an automatically operating interlock preventing access to the levering-in rod""s hex drive unless the cabinet door is closed.
It is another aspect of the present invention to provide a locking plate that is biased towards a position wherein rearward movement of the levering-in locking plate is resisted unless the cabinet door is closed.
It is a further aspect of the present invention to provide an automatically operating interlock mechanism for electrical cabinets including a spring-biased locking plated controlled by the position of the cabinet door, and controlling access to the levering-in rod.
It is another aspect of the present invention to provide an automatically operating interlock that is simpler, more reliable, and easier to manufacture than other interlocks.
These and other aspects of the present invention will become apparent through the following description and drawings.